Pietro Gambardella

Pietro Gambardella

Affiliation: ETH Zürich

Research Interests: Magnetism and Interface Physics

Title: From Spintronic Devices to Quantum Spin Torques

Abstract: Spin torques are central to spintronics, enabling current-induced magnetization switching, domain wall motion, and resonant magnetic oscillations in nanoscale devices. While most studies describe spin torques in semi-classical terms, probing their action at the level of a single spin reveals their fundamentally quantum nature. Electron paramagnetic resonance (EPR) performed via scanning tunnelling microscopy (STM) offers coherent control over individual spins along with direct insight into their interaction with electric currents and the surrounding environment. In this talk, I will show that EPR of a single spin in a pentacene molecule can be driven by a time-dependent spin-polarized current injected from the STM tip. Depending on the tunnelling regime, the molecular spin exhibits either coherent or incoherent dynamics, whereby spin rotations and decoherence are controlled by the applied voltage and current. These results offer a unique perspective on how electric currents influence quantum spin states, in contrast with the established action of time-dependent electromagnetic fields. Spin torques also enable to excite EPR in regimes where the thermal spin polarization is too low to yield an observable EPR signal by an oscillating magnetic field.